1. Technical Field
The present inventions relate to improved reliability and safety of electrical initiators for explosive devices.
2. Background Art
Electro-explosive initiation devices are commonly used in the aerospace, military, automotive and oil and gas industries in explosive systems to perform perforating and cutting operations. These initiation devices act as the starting element to begin the explosive sequence.
Conventional Semiconductor Bridge (SCB) explosive devices utilize a semiconductor bridge element in intimate contact with an energetic material as an initiator. The bridge is used to covert electrical pulse energy into thermal energy which is then used to release the chemical energy of the energetic material. When sufficient electrical impulse is applied, the semiconductor bridge vaporizes, generating a rapid release of heated particles (plasma event). At the desired electrical energy level the plasma event initiates a chemical breakdown (deflagration reaction) in the surrounding energetic material if the material is of the type that is sensitive to plasma events.
Common electrical hazards for electroexplosive initiators include low level stray currents and RF signals. Unless protected by circuitry or other means such as electromagnetic shields, the electrical hazards could possibly induce current flow across the semiconductor bridge causing ohmic (resistance) heating of the bridge element. If the energetic material in contact with the bridge is sufficiently insensitive, it acts as a heat sink and thus allows the bridge to “burn out” in a passive manner without initiating a plasma event. In this instance the initiator is now in the dudded condition and not able to function. If the energetic material in contact with the bridge element is sufficiently sensitive, then the simple ohmic heating (i.e., not plasma heating) could cause chemical reaction thus initiating the electro-explosive device.
In prior art plasma devices, such as Halliburton's Rig Environment Detonator (RED®), the semiconductor bridge is in intimate contact with an insensitive pyrotechnic material. However, to further enhance its safety, the present invention calls for the semiconductor bridge element to be separated from the energetic material regardless of whether it is sensitive or insensitive. By introducing the separation, the effects of ohmic heating are removed. The separation gap, however, causes initiation by plasma heating to become less reliable since the hot plasma particles must traverse the gap and thus undergo cooling effects. If the gap is too great, the normal “plasma mode” of initiation will fail thus leading to a dudded device.
While plasma gap type initiators have improved safety characteristics, separating the semiconductor bridge from the energetic material produces a less reliable initiator. In addition plasma gap type initiators are limited in that the energetic material must be of the type that is sufficiently sensitive to plasma events.
Therefore there is a need for an initiator with improved safety and reliability and one that can be used with a wider variety of energetic materials.